1. Field of the Invention
This invention relates to the fabrication of ceramic substrates and particularly to an automated apparatus and method for breaking a prescored ceramic substrate plate into a plurality of individual substrates in a manner which simulates the action of breaking the plate by hand.
2. Description of the Prior Art
The typical ceramics used in fabricating substrates for miniature thick film, as well as some thin films, resistor and capacitor components or circuits are composed of 92% to 99% alumina ceramic (Al.sub.2 O.sub.3), which is amorphous and very hard. The substrates typically are rectangular in shape, between 0.015 to 0.035 inches thick, less than 1.5 inches long and less than 1/2 of an inch wide.
Impedance films for such resistor and capacitor components (and even inductor components), are conventionally formed on one surface of the substrate by evaporation in the case of thin film components or by conventional silk screen and firing techniques in the case of thick film components. When high volume fabrication is required, the components are usually produced by silk screening the patterns in multiple images (e.g., 2 to 60 or more) in one pass on a large sheet or plate of ceramic material. The large ceramic plate can be prescored between pattern areas by green scoring the plate before it is sintered or by laser scoring the plate to size after it is sintered. The plate can also be postscored to size after the components have been deposited thereon. The scored individual substrates, with their deposited components, are then broken off of the larger ceramic plate.
The methods currently used in mass production applications for breaking the individual substrates off of a larger ceramic plate are generally variations of two basic methods. In the first basic method, the plate is held stationary with a single unit extending over a break edge and then pressure is applied to the scribed side of the extended piece in order to break off the extended unit. In the second basic method, the plate is placed, scribed side down, on a resilient surface and a roller is rolled across the plate with an appropriate pressure to break off successive units.
To date, however, the prior art breaking methods have been characterized by a lack of precise control over the application of pressures, thereby producing decidedly inferior results, in terms of the percentage of substandard or ruined substrates due to incorrect fractures, than those results achieved by manually breaking the individual pieces. However, such manual breaking is a slow and laborious method at best. Thus, until the present invention, high quality production could be achieved only by sacrificing the economy and efficiency of mass production.
One attempt to avoid the trade-off between quantity and quality in ceramic substrate production is described in U.S. Pat. No. 3,507,430. This patent discloses a tool for snapping a prescored ceramic substrate plate into separate substrates. The tool has members which are seated within W-shaped grooves in the plate. The application of pressure to the members snaps a separate substrate off of the plate by removing the central portion of the W. While, in terms of speed, this is an advance over manually breaking the ceramic plate into separate substrates, the need for prescoring the plate with W-shaped grooves, rather than V-shaped grooves, adds to the expense of fabrication, over and above the expense of the specially fabricated tool required.
Various other devices are known in the art for breaking scored workpieces into smaller pieces with both speed and accuracy.
Each of the U.S. Pat. Nos. 2,042,819; 3,141,592; and 4,046,300 discloses an apparatus for breaking scored glass sheets. In U.S. Pat. No. 2,042,819, a scored glass sheet is broken along each scored line as that scored line moves between rollers. In U.S. Pat. No. 3,141,592, a scored glass sheet is broken along each scored line by the fulcrum action of a roller against one end of the sheet as each scored line of the sheet moves between two breaker rollers. In U.S. Pat. No. 4,046,300, a scored glass sheet on a conveyor, stopped over a breakout template, is broken by the movement of a roller over the scored line of the glass.
In a similar manner, each of the U.S. Pat. Nos. 3,105,623; 3,601,296; and 3,870,196 discloses methods and devices for breaking crystalline semiconductor materials. In each of U.S. Pat. Nos. 3,105,623 and 3,601,296 a prescored crystalline semiconductor material, mounted on a resilient flat surface, is broken along each scored line as that scored line moves beneath a roller. In U.S. Pat. No. 3,870,196 a prescored crystalline semiconductor wafer, mounted on a flat resilient pad, is broken along the prescored lines as a roller is moved across the wafer.
However, the above-described methods and devices for breaking glass sheets or crystalline semiconductor materials into smaller pieces are not readily adapted for use on ceramics, due to the unique properties of ceramic materials. The glass breaking devices are specifically used for breaking off relatively large pieces of a material which breaks with far less pressure than does alumina ceramic. The semiconductor breaking devices are designed for operation on material which is, as previously noted, crystalline in nature and which, therefore, easily cleaves along prescored lines. On the other hand, amorphous alumina ceramic lacks such natural cleavage.
None of the above-described prior art devices and methods teaches an automated apparatus or method for selectively breaking a prescored ceramic substrate plate into a plurality of individual substrates in a manner which simulates the action of breaking the plate by hand.